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The K7RA Solar Update

03/27/2009

Every day I check the 45 day forecast of planetary A index and solar flux from NOAA and the US Air Force. For quite some time now, the solar flux forecast has been the same: The projection shows 45 days of solar flux at 70, with no variation. I look at this because there is so little sunspot activity and I hope that any increase in predicted solar flux values may coincide with renewed sunspot activity. But this method hasn't worked out very well in the past year or so.

When I looked at this on Wednesday night, March 25, the 10.7 cm flux forecast showed 70 for March 26-27, then bumping up to 72 for March 28-31 and then back to 70 for all of April and beyond. This is not much increase in activity, but with such a quiet Sun for the past few years, we become sensitive to small changes -- and even optimistic at times. Last night, Thursday, March 26, the prediction was nearly the same, except with the solar flux of 72 lasting two more days, through April 2.

You can look at he forecasts here; click on "Alerts, Forecasts and Summaries," then "USAF 45-day Ap and 10.7 cm Flux Forecasts." The new daily forecast is posted around 2100 UTC, but often doesn't appear in the list until later. If you suspect this is the case, just click on the latest available date, then edit the URL at the top of your Web browser to reflect the current date. So if it is Friday, March 27, and the latest listing you see is for March 26, just click on that link, and at the end of the URL change /032645DF.txt to /032745DF.txt and hit the Enter key. If that day's forecast has been uploaded, it should pop up when you hack the Web address using these instructions.

Currently, USAF and NOAA predict a planetary A index of 8 for today, March 27, then leveling off at 5 (a very quiet, stable level) until April 9-10 when it jumps to 15, then 10. Geophysical Institute Prague predicts quiet to unsettled conditions March 27, quiet March 28-29, quiet to unsettled March 30-31 and back to quiet for April 1-2. Sunspot numbers for March 19 through 25 were 0, 0, 0, 0, 0, 0 and 0 with a mean of 0. The 10.7 cm flux was 69.1, 68.7, 70.1, 68.7, 68, 69.1, and 68.5 with a mean of 68.9. The estimated planetary A indices were 3, 4, 8, 4, 3, 8 and 10 with a mean of 5.7. The estimated mid-latitude A indices were 3, 2, 5, 4, 2, 6 and 7 with a mean of 4.1.

Early on March 26, Spaceweather.com reported a new "proto-sunspot" seen "struggling to emerge" at high latitude, making it a Solar Cycle 24 spot. The same site reported the Solar and Heliospheric Observatory (SOHO) is monitoring "intense activity on the Sun's northeastern limb." The following day, Spaceweather.com repeated a common refrain heard lately after some activity begins to emerge: "Yesterday's proto-sunspot failed to emerge. The Sun is blank."

The NASA STEREO (Solar TErrestrial RElations Observatory) mission will eventually enable views of the entire Sun, so we will know in advance about emerging solar activity that is outside Earth's view. The two spacecraft orbit the Sun similar to Earth, but one leads the Earth and the other follows. The leading spacecraft A travels faster than the trailing spacecraft B, and because of this, the angle of the two relative to each other gradually increases over time. The craft were launched October 26, 2006 and they reached quadrature, or 90 degrees separation, 62 days ago on January 24, 2009.

Spacecraft A takes 347 days to complete an orbit of the Sun, and spacecraft B takes 387 days. They separate from each other at a rate of about 44 degrees per year. View their current positions, updated hourly, relative to Earth, the Sun, Venus and Mercury. Click on the STEREO Orbit Tool link, and you can view a similar image for any date and time from the launch date through the end of 2015.

NASA has a dense, single page pdf document describing the mission, and while we can't recommend Wikipedia as an always-reliable resource (its immediately changeable nature drives teachers and reference librarians crazy), the Wikipedia community seems to have a good information page on STEREO. Other NASA resources are here and here. Johns Hopkins University Applied Physics Laboratory has information, too.

This weekend is the CQ World Wide WPX SSB Contest. Perhaps we'll get lucky with some worldwide propagation. The chance of disruption by any geomagnetic activity seems remote.

Finally, Kenneth Beck, WI7B of Kennewick, Washington responded to last week's musings about east and west on the Sun. Referencing an image, he wrote, "It always seemed to me to be clearer when I realize that the Sun rotates around its axis in the same direction as the Earth. This is the 'right-hand rule,' with your thumb pointing toward the 'north.' With that perspective, look up at the sky (you can stand, sit or crawl on your knees for this thought experiment), hold up your right hand with the thumb pointing up to the sky, and then rotate it. Sunspots will travel in the direction of your fingers, counter-clockwise around your thumb. Better yet, hold a full mug of beer in your right hand and turn it. The bubbles in the beer will turn just like sunspots. Now drink!"

Amateur solar observer Tad Cook, K7RA, of Seattle, Washington, provides this weekly report on solar conditions and propagation. This report also is available via W1AW every Friday, and an abbreviated version appears in The ARRL Letter. Check here for a detailed explanation of the numbers used in this bulletin. An archive of past propagation bulletins can be found here. You can find monthly propagation charts between four USA regions and 12 overseas locations here. Readers may contact the author via e-mail.



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